USE OF HORSEPOWER TABLES 25 



page 108, which shows the relative cross-sectional area of belts 

 of different sizes. As the horsepower transmitted under a 

 given set of conditions varies directly with the cross-sectional 

 area of the belt, a simple multiplication of the figure obtained 

 from the horsepower table by the constant in the table of 

 relative areas will give the desired result. The same state- 

 ment applies to the tension values. Multiplying the initial 

 and minimum tension values as given in the horsepower 

 tables by the constant from the table of relative areas will 

 give the total tension under which any belt should be put up, 

 and the total tension below which it should not be allowed 

 to fall in service and at which it should be shortened and 

 retightened. 



Examples in the Use of the Tables. The following ex- 

 amples will make clear the use of the tables : 



Example I. The three steps of a lathe cone pulley have 

 diameters respectively of 14, 16 and 18 in. The face of each 

 step is 5 in. The countershaft cone has the same diameters, 

 and rotates at a speed of no r.p.m. The distance between 

 the center lines of the machine spindle and the countershaft 

 is 8 ft. What size of belt is necessary to deliver 3 horsepower 

 to the machine cone when the belt is on the largest step of 

 that cone? What horsepower will be deliveied to it when 

 the belt is on the smallest step of the machine cone? What 

 will be the maximum and minimum initial tension in the belt 

 under which it should be put up, and below which it should 

 not be allowed to fall in service? 



The difference between the diameter of the largest step 

 of the macnine cone and the smallest step of the counter- 

 shaft cone is 4 in. Referring to the arc of contact table on 

 page 96, we find that for a 4-in. difference in diameter, a 

 center-line distance of 8 ft. will give an arc of contact on the 

 smaller pulley of 178 degrees. For all practical purposes 

 this can be regarded as 180 degrees. The velocity table on 

 page 103 shows that a i4-in. pulley at no r.p.m. will give a 



